The present invention relates generally to pressure responsive valve assemblies and in particular to such a valve assembly adapted for use in a decanting apparatus in a wastewater treatment facility.
Certain wastewater treatment processes, especially those utilizing sequential batch reactor techniques or processes, require that clarified fluid be periodically withdrawn from the reactor or digester within which the process is occurring. During certain cycles within the reactor, especially mix cycles, sludge is agitated with all of the fluid in the reactor in order to mix organic degrading bacteria with organic materials in the water being treated. It is important that the decanting system not allow the sludge to enter the decanter during the mix cycles or have sludge settle within the decanting system so that when the sludge is settled and clarified liquid is withdrawn from the reactor, no sludge is withdrawn with the clarified liquid. Sludge discharged with the clarified liquid causes substantial downstream pollution.
One of the major problems with certain prior art decanter systems for use in batch reactors has been that a receiver for the decanter has had the interior thereof open to fluid within the reactor during sludge mixing cycles. When the sludge is being mixed with the incoming effluent and the entire reactor is in a generally mixed state, sludge is near the top of the reactor as well as the bottom. If the receiver is open at this time, the sludge usually enters the receiver and settles therein during settling cycles. Thereafter, when the clarified fluid is withdrawn through the receiver, the sludge that is within the receiver is entrained with the clarified fluid to pollute the effluent.
Over the years, engineers have developed various devices to solve this problem. In one such device, an initial quantity of clarified effluent removed from the reactor during each decanting cycle is flushed back into the reactor so as to return the entrained sludge. However, such a solution requires a pump and control mechanisms which complicate the system and can easily fail leading to substantial downstream pollution.
Other attempts to resolve the problem of sludge settling within the receiver have been directed to physically removing the receiver from the tank during mixing cycles. This typically requires a cumbersome and expensive structure which is suitably strong to hold a decanting system out of the reactor fluid during the mix cycle. In addition, where freezing is likely to occur, fluid within the decanting structure may freeze if raised from the liquid in the reactor, or the fluid level at the top of the reactor may freeze which may make it difficult or impossible to raise and lower the decanting structure.
Finally, various types of pressure responsive valves or flaps have been placed in the openings to the decanting system to keep sludge out of the system when the contents of the reactor are being mixed. While such valves or flaps have reduced the sludge in the decanted fluid, none have been successful in keeping sludge sufficiently out of the effluent to satisfy many pollution control requirements, especially at relatively high wastewater flow rates. In particular, such prior art valves often have provided surfaces onto which the entrained sludge may settle during the settling cycles. Then during decanting cycles, the sludge becomes entrained in the clarified effluent withdrawn from the reactor through the receiver. In many pressure responsive valves, the structure forming the valve seat extends beyond the interface of the valve member with the valve seat. If such a valve were used in a decanting apparatus for a wastewater treatment reactor, the structure forming the valve seat would extend beyond the valve member into the reactor providing significant surface area for sludge to settle on during the settling cycles.